A machine for converting a substrate is intended for the production of packaging. In this machine, an initial flat substrate, such as a continuous web of cardboard, is unrolled and printed on by a printing station comprising one or more printer units. The flat substrate is then transferred into an introduction unit and then into an embossing unit, possibly followed by a scoring unit. The flat substrate is then cut in a cutting unit. After ejection of the scrap areas, the preforms obtained are sectioned in order to obtain individual boxes.
The rotary conversion may be an embossing unit, a scoring unit, a cutting unit, a scrap-ejection unit, or a printer unit. Each rotary conversion unit comprises a cylindrical upper conversion tool and a cylindrical lower conversion tool, between which the flat substrate passes in order to be converted. In operation, the rotary conversion tools rotate at the same speed but in opposite directions to one another. The flat substrate passes through the gap situated between the rotary tools, which form a relief by embossing, form a relief by scoring, cut the flat substrate into preforms by rotary cutting, eject the scrap, or print a pattern during printing.
The cylinder changing operations have been found to be time-consuming and tedious. The operator must mechanically disconnect the cylinder in order to remove it from its drive mechanism. Then, the operator must extract the cylinder from the conversion machine and fit the new cylinder in the conversion machine by reconnecting it to its drive. The weight of a cylinder is high, around 50 kg to 2000 kg. In order to extract it, the operator must lift the cylinder with the aid of a hoist.
Because of its fairly high weight, a cylinder cannot be changed very quickly. Moreover, numerous tool changes may be necessary to obtain a very large number of boxes that are different from one another. These tools have to be ordered a long time in advance, which is becoming incompatible with the production changes that are currently required. In addition, tools are relatively expensive to produce and they only become cost-effective with an extremely large output.
Therefore, some conversion units have rotary tools made up of a mandrel and a removable sleeve carrying the form for carrying out the conversion that is able to be fitted on the mandrel. All that is necessary is to change the sleeve rather than the entire rotary tool. This makes it easier to change the tool because of the low weight of the sleeve and reduces costs since the sleeve is less expensive.
The passage of the flat substrate through the successive conversion units tends to heat the flat substrate, notably as it passes through the printer units. The heated flat substrate in turn heats the rotary tools since the latter, which are generally metallic, are very good conductors of heat. The dimensions of a sleeve are thus generally provided in order to limit the play between the sleeve and the mandrel during conversion operations. A resulting difficulty is that when the conversion unit is stopped, the sleeve, which has better thermal conductivity than the mandrel, cools down more quickly than the latter. It is then difficult to remove the sleeve from the mandrel.